In an interview with The Sydney Morning Herald, Dr Sims explained that at this time of our menstrual cycle, our hormone levels drop and this affects everything from how cool you feel to how easily you access energy stores.

"Pain tolerance is increased; time to fatigue is increased; she has a lower core temperature and greater plasma volume, so she can sweat more and stay cool longer, and from a metabolic state, a woman's body can tap into more carbohydrate stores and recover faster, as compared to the high hormone phase that leads into her period," Dr Sims explained.

So how exactly do you make the most of this, ahem, period?

Dr Sims said that this is the perfect time to be heading to the slightly intimidating-sounding HIIT classes at the gym or to try for your personal best time on the treadmill or at a running event.

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Celebrity gym selfies.

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"It's during this low-hormone phase that women should aim to hit high-intensity training sessions hard, try for PRs in power and speed activities, and optimise recovery through nutrition," she said.

However, personal trainer Nardia Norman added that pushing yourself to exercise intensely when you don't feel up to it, isn't a good idea.

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The former personal trainer of the year said abdominal pain or bloating negatively affects your abdominal muscles. She said this could affect your stability and lead to an unstable spine and possibly an injury.

Keen to work with your menstrual cycle? You can also tailor your workout to your hormone levels during the rest of the month too.

The next two weeks following your period is the best time to be hitting the weights and taking on intense training.

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Norman explains this is because the female hormone oestrogen is at its highest levels, giving you a natural energy boost.

During the last fortnight, known as the luteal phase, your oestrogen levels dip and as your progesterone rises.

That's the time to back off on the weight training, according to Norman.

Instead, go for a long run and work on your endurance or cardio. This is because women tend to have more stamina at this time. She said it's also a good time to eat more protein to aid recovery.